Vehicle-actuated devices located in vehicle parking areas for preventing unauthorized removal and/or producing an alarm when removed without authorization are known in the art. For example, Selby U.S. Pat. No. 3,757,916 shows barrier plates which are moved into position behind the front wheel of a vehicle when the latter is parked within a given parking area to prevent the vehicle from being removed until the correct parking fee has been deposited. U.S. Pat. No. 3,986,591 shows a hood which is automatically raised beneath the vehicle when the vehicle is parked in a predetermined parking area to a position of engagement with the underside of the vehicle such as to prevent the vehicle from being removed without first depositing the correct parking fee. Waldman U.S. Pat. No. 2,815,842 shows a device which must be attached by the driver to the vehicle at the time of parking to start the meter and which, when detached, resets the meter to a zero position. Cherico U.S. Pat. No. 3,824,536 shows a wheel block adapted to be placed in blocking engagement with a wheel which is operable if the wheel is moved away from it to produce an alarm. U.S. Pat. Nos. 3,781,861; 3,824,540 and 3,866,205 show various kinds of bicycle locks and alarms which are operated if an attempt is made to remove the lock. The anti-theft system of this invention, unlike the aforesaid patents, is not designed to physically constrain the vehicle, but, on the contrary, is designed to produce a visual and/or audible system with minimal circuitry, the latter being so designed that the system itself cannot be actuated in the absence of a parked vehicle.